The invention relates to a projection device comprising at least a light source, at least a light-modulation panel preceding the light source, and a polarization-separating means arranged between the light source and the light-modulation panel for separating light from the light source into first and second light beams having a first and a second direction of polarization, respectively.
The invention also relates to an integrator plate suitable for such a projection device.
In such a projection device known from U.S. Pat. No. 5,900,977, the polarization-separating means comprises a refractive filter which passes light having the first direction of polarization and deflects, at an angle, light having a second direction of polarization perpendicular to the first direction.
In the projection device described in said United States patent, the light beams of different directions of polarization are imaged by a polarization rotation layer on a further polarization-separating means and subsequently directed onto the light-modulation panel. A drawback of such a projection device is that the light source is imaged only once on the light-modulation panel so that the light distribution across the light-modulation panel is not uniform.
It is an object of the invention to provide a projection device in which a uniform light distribution across the light-modulation panel is obtained with a relatively high luminance.
In the projection device according to the invention, this object is achieved in that the projection device further comprises first and second integrator plates comprising lens elements arranged between the polarization-separating means and the light-modulation panel, and polarization-converting means arranged opposite the second integrator plate, each lens element of the second integrator plate having a first portion on which a light beam having the first direction of polarization is imaged by the first integrator plate, and a juxtaposed, second portion on which a second light beam having the second direction of polarization is imaged, the polarization-converting means being arranged at least opposite the first portions.
The light from the light source is split up into two light beams having different directions of polarization by the first integrator plate comprising the polarization-separating means and the lens elements. Subsequently, each lens element of the first integrator plate is imaged on an associated lens element of the second integrator plate. As a result of the different directions at which the light beams having the different directions of polarization reach a lens element of the first integrator plate, the images on the associated lens element of the second integrator plate of the light beams having the different directions of polarization are also different. All light beams imaged on the first portions of the lens elements have, however, the same direction of polarization which is subsequently converted by means of the polarization-converting means into the same direction of polarization as the direction of polarization of the two light beams imaged on the second portions.
The light beam from the light source is imaged one across the other a number of times by the lens elements of the first and second integrator plates, so that a satisfactory light distribution across the light-modulation panel is obtained.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.